1. Field of the Invention
The present invention relates to a method for producing an integrated optical device.
2. Description of the Related Art
Patent Reference 1 (Japanese Unexamined Patent Application Publication No. 2005-55764) and Patent Reference 2 (Japanese Unexamined Patent Application Publication No. 2002-243964) describe a method for producing an integrated optical device having a butt-joint structure. In the method describing in Patent Reference 1, a first waveguide having a stacked semiconductor layer including an InGaAsP active layer and a p-type InP cladding layer grown on an InP substrate is formed. Then, a second waveguide having a stacked semiconductor layer including an InGaAsP core layer and a p-type InP cladding layer is formed adjacent to the first waveguide on the InP substrate. Before forming the second waveguide, the InGaAsP active layer and p-type InP cladding layer of the first waveguide is etched by wet etching through an etching mask. In this wet etching, a recess is formed under the etching mask. By forming the recess, a rising of the InGaAsP core layer and p-type cladding layer is suppressed at growing the second waveguide.
In the method describing in Patent Reference 2, a first lower guiding layer, an active layer, a first upper guiding layer, and a first upper cladding layer are sequentially grown on an InP substrate. The first lower guiding layer, the active layer, and the first upper guiding layer constitute a first waveguide layer. Then, an etching mask is formed on the first upper cladding layer. Portions of the first upper cladding layer, the first upper guiding layer, and the active layer are removed by dry etching through the etching mask. After this dry-etching process, the first waveguide layer is etched by wet etching through the etching mask. At this time, a side surface of the first waveguide layer undergoes side etching. On the InP substrate having been exposed by the wet etching, a second waveguide layer and a second upper cladding layer are sequentially grown. Thus, the butt-joint coupling between the first waveguide layer and the second waveguide layer is achieved.